Many rotary electric machines as, for example, generators, have a fluid flow path through the rotor. In most cases, a liquid such as oil is circulated through the flow path to provide the dual function of cooling rotor windings to thereby increase the capacity of the machine and to provide for lubrication of bearings journalling the rotor. In some instances, the construction will utilize but one or the other of the two above specified functions, while in others, the fluid may be discharged from the rotor to impinge on stator winding end turns to provide an additional cooling function.
Invariably, impurities, most notably, very small particulates of metal or the like are found in the liquid being circulated. Where the liquid is serving a lubricating function, the presence of such particulates accelerate bearing wear resulting in increased maintenance and/or decreased machine life. Though not as obvious a problem, such foreign material will also shorten machine life where the liquid is employed as a coolant, particularly in those rotary electric machines wherein the coolant passages for winding are formed by the interstices between the windings themselves.
Over a period of time, the particulates lodge in the interstices and impede coolant flow. As particle build-up continues, coolant flow is progressively lessened with the consequence that hot spots in the windings develop. Ultimately, the insulation on the windings will fail at the hot spot causing short circuiting and machine failure.
It has thus been proposed to filter the coolant. See, for example, U.S. Pat. No. 3,242,360 issued Mar. 22, 1966 to Carle wherein what appears to be a conventional filter is installed in the coolant flow path of a submersible pump.
While this approach may work well in many applications, it is not satisfactory in many instances where the rotary electric machine is one which operates at high speed. For example, aircraft generators are typically operated at 12,000 rpm or more and in such operation, extremely fine oil contaminants which may escape a conventional filter media are subjected to high gravitational loads during operation due to centrifugal force. The large forces tending to move such fine contaminants are disposed to move them radially outwardly and since, for convenience, most rotary electric machines locate coolant inlets and outlets to the rotor on the axis of rotation, and yet have coolant flow paths spaced from the axis of rotation, it is extremely difficult, if not impossible, to entrain such fine particles in the coolant stream sufficiently to move them radially inwardly within the rotor the fluid outlet therefrom. As a consequence, the coolant passages displaced from the axis of rotation slowly become plugged ultimately resulting in failure of the machine.
The present invention is directed to overcoming one or more of the above problems.